The present invention relates to a device for measuring the number of bacteria in superpure water, and more particularly to a device for measuring the number of bacteria in superpure water used for manufacturing semiconductor devices or the like.
In water quality inspection, it is essential to detect both the types of bacteria in the water under test and how many bacteria are included in a given unit quantity of the water. Detection of the number of bacteria in water is absolutely necessary for superpure water such as is required in manufacturing medicines in which the number of bacteria must be limited to an extremely small value, or in the case of manufacturing semiconductor devices (especially super-LSI semiconductor devices) in which the number of bacteria per 10 cc of superpure water is limited to ten or less.
In a conventional method of detecting the number of bacteria in a unit quantity of superpure water, a sample of the water is extracted and the bacteria in the sample are cultivated to allow them to multiply. The bacteria thus treated are filtered and stained, and the stained bacteria are counted under a microscope.
When such a detecting method is employed, it takes about seven days to accomplish all of the steps from sampling the superpure water to counting the number of bacteria. If the quality of the superpure water is thereby determined unacceptable, the semiconductor devices manufactured during the detection period must be discarded, which increases the average manufacturing cost of the devices.
The present inventors have proposed a bacteria counter which can detect the number of bacteria in water under test in an extremely short period of time, with the result that the manufacturing cost of semiconductor devices or the like can be reduced.
The bacteria counter proposed by the present inventors fundamentally is composed of a transparent measurement chamber into which the water under test is introduced and to which acridine orange or a derivative thereof is added to react with the bacteria contained in the water under test to form reaction products, an exciting light source for applying an exciting light beam to the water under test in the measurement chamber to cause the reaction products to fluoresce, a photoelectric converter for detecting the amount of fluorescent light so produced, and an arithmetic unit for converting the output of the photoelectric converter to the corresponding number of bacteria per unit quantity of water.
The present inventors have found that, where fluorescein diacetate, ethidium bromide, or ethidium iodide, is used as the reagent added to the water under test to react with the bacteria in the water to form reaction products which fluoresce when an exciting light beam is applied, the reagent reacted with the bacteria produces fluorescence, but not the free reagent in the pure water.